Applicator Reconstruction in Gynecological Brachytherapy on MRI

Interstitial Brachytherapy and Applicators Libraries

Antonio Otal Palacín

Hospital Universitari Arnau de Vilanova (Lleida)

Summary (Actualizar)

• Brachytherapy
• Gynecological Brachytherapy
• Imaging modalities: CT vs MRI
• Applicator reconstruction
  • Applicators with interstitial part
• Virtual planning

Notes

Brachytherapy

Brachytherapy, also known as internal radiation therapy, is a type of radiation therapy in which a radioactive substance is placed inside or directly next to the area requiring treatment. This allows for a high dose of radiation to be delivered to the tumor or other affected tissue, while minimizing exposure to healthy surrounding tissue. Brachytherapy is often used to treat cancers of the prostate, breast, cervix, and head and neck. It can also be used to treat other conditions, such as non-melanoma skin cancer and gynecological disorders.

Brachytherapy vs External Beam Radiotherapy (Tele-therapy)

TrueBeam platform
Varian Medical Systems

MicroSelectron
Elekta

Brachytherapy: In brachytherapy, radioactive sources (such as seeds, pellets, or wires) are placed directly inside or near the tumor site. The radiation is delivered from within the body, allowing for precise targeting of the tumor while minimizing radiation exposure to surrounding healthy tissues. External Beam Radiotherapy: With external beam radiotherapy, the radiation is generated from a machine located outside the body. High-energy X-ray beams or other forms of radiation are directed at the tumor site from various angles.

Brachytherapy modalities

High-Dose Rate (HDR)

Low-Dose Rate (LDR)

Pulsed-Dose Rate (PDR)

High-Dose Rate (HDR) Brachytherapy:

Energy: HDR brachytherapy uses high-energy radioactive sources, such as iridium-192 or cobalt-60. Rate: HDR brachytherapy delivers a high dose of radiation over a short period, typically in fractions given at multiple treatment sessions. The radioactive sources are temporarily placed inside the body using applicators or catheters, and a computer-controlled machine called an afterloader moves the sources to the treatment area. Low-Dose Rate (LDR) Brachytherapy:

Energy: LDR brachytherapy employs low-energy radioactive sources, usually in the form of radioactive seeds or pellets, such as iodine-125 or palladium-103. Rate: LDR brachytherapy delivers a continuous low dose of radiation over an extended period. The radioactive sources are permanently or semi-permanently implanted in or near the tumor site. Over time, the radiation emitted by the sources gradually decreases, providing a prolonged but low-dose treatment. Pulsed-Dose Rate (PDR) Brachytherapy:

Energy: PDR brachytherapy uses radioactive sources with intermediate energy levels, similar to HDR brachytherapy. Common isotopes used include iridium-192 or cesium-137. Rate: PDR brachytherapy delivers radiation in pulses or intervals. The sources are temporarily placed inside the body, and the treatment is administered using an afterloader machine that controls the timing and duration of the radiation pulses. The pulses allow for periods of radiation delivery and intervals for normal tissue recovery.

Brachytherapy modalities

High-Dose Rate (HDR)

Notes

Brachytherapy application

Cavum

Gynecological

Notes

Source Positions

Notes

Dose distribution

Notes

Differences between intracavitary and interstitial brachytherapy

Intracavitary brachytherapy

Interstitial brachytherapy

Notes

Brachytherapy workflow

Image adquisition

Contouring

Reconstruction

Dosimetry

Treatment delivery

• Imaging: The process begins with imaging studies, such as CT (computed tomography) or MRI (magnetic resonance imaging), to visualize the tumor and surrounding structures accurately.

• Contouring: Radiation oncologists and medical physicists contour or delineate the tumor and nearby critical structures (organs at risk) on the imaging scans. This step helps in designing the treatment plan and ensuring accurate dose delivery.

• Reconstruction

• Dosimetry

• Radiation Delivery: The radioactive sources are temporarily inserted into the catheters or applicators, delivering a high dose of radiation to the tumor and surrounding tissues. The treatment is carefully controlled and monitored by the medical team.

Brachytherapy workflow

Reconstruction

Commons Locations

Prostate

Gynecological

Breast

Head and Neck

Ophthalmic

Prostate : This is one of the most common applications of brachytherapy. It involves the placement of tiny radioactive seeds directly into the prostate gland. The procedure is typically performed in an operating room or an outpatient clinic.

Gynecological : Brachytherapy can be used to treat gynecological cancers such as cervical, endometrial, or vaginal cancer. The treatment may involve the placement of radioactive sources directly into the vagina (intravaginal brachytherapy) or into the uterus (intracavitary brachytherapy). These procedures are usually performed in a radiation oncology department.

Breast : In some cases of early-stage breast cancer, brachytherapy may be used as an alternative to whole-breast radiation therapy. It involves the insertion of catheters or a specialized device with radioactive sources into the breast tissue. The treatment is typically performed in a radiation oncology department.

Head and Neck : Brachytherapy can be utilized to treat certain head and neck cancers, such as tongue or oral cavity cancers. It involves the placement of radioactive sources directly into the tumor or the surgical cavity. The procedure is generally performed in a radiation oncology department or an operating room.

Ophthalmic : Brachytherapy can be used to treat certain ocular tumors, such as choroidal melanoma. Radioactive plaques or seeds are surgically implanted on the sclera (white part of the eye) near the tumor. The treatment is typically performed in a specialized eye clinic or hospital.

Commons Locations

Gynecological

Gynecological Brachytherapy HDR

Notes

Indications

Cervical Cancer

Endometrial Cancer

Vaginal Cancer

Notes

Indications

Cervical Cancer

MRI golden standart

MRI vs CT: Cervix

MRI vs CT: Applicator

Reconstruction in Brachytherapy

Notes

Problem Statement

• The problem is a conversion from 3D to 1D due to the constraints involved.
• Most distal position as origin of l parameter.

Notes

Impact on dose distribution

DVH parameters

• Bladder and rectum in ant-pos direction: 5%-6% per mm
• Rest of organs and directions: 4% per mm

Warning

Systematic errors of a few millimetres can lead to significant deviations (More than 10%).

Notes

Direct Reconstruction (DR)

The most distal stopping position (tip position) and the trajectory of the source on the image must be identified.

Pros

• This is the most intuitive and straightforward way to do it.

Cons

• Trajectory and/or tip position of the source may not be visible
• Slice thickness

Notes

Dummies CT

Dummies MRI

Caution

There are no commercial dummies for MRI compatible needles.

Applicator Libraries (AP)

Notes

Limitations

When using several rigid applicators each applicator should be imported separately, since there is a risk that the position of the applicators in relation to each other could change inside the patient.

Notes

Focus on MRI-compatible applicators

Notes

Plastic applicators

Notes

Metallic applicators (titanium)

Notes

Imaging Modalities
CT vs MRI

Notes

The use of imaging in brachytherapy

Notes

CT-guided brachytherapy

Notes

Transition to MRI

Notes

Image registration

Notes

MRI-guided exclusive brachytherapy

Notes

Virtual
Planning

Notes

Presentation of the problem

Notes

The Benidorm applicator

Notes

Contributions

ALFIM2016

Notes

Characterization of a Gynaecological Titanium Applicator for Direct Reconstruction on MRI (AAPM2019)

Notes

Novel Semi-Automatic Reconstruction Method for Plastic Gynaecological Applicators (AAPM2019)

Notes

A novel tool for the reconstruction of the Utrecht applicator on MRI (ABS2021)

Notes